Synthesis of the First α‐Methylene‐β‐peroxylactone—Regiospecific Ene Reaction of 1 O 2 with α,β‐Unsaturated Carboxylic Acids

5‐Methyl‐4‐methylene‐1,2‐dioxolane‐3‐one 2 exhibits unexpectedly high thermal stability . The first α‐methylene‐β‐peroxylactone was obtained by regiospecific photooxygenation of the α,β‐unsaturated carboxylic acid 1 to give the hydroperoxide followed by acid‐catalyzed dehydration.